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Ten thousand years of bitumen transport in the lower Athabasca River, Canada

  • Author / Creator
    Kwan, Kin Hung
  • The lower Athabasca River valley in northeastern Alberta, famous for oil sands mining, was also the site of one of North America largest Ice Age floods. During deglaciation, a large proglacial lake, Lake Agassiz, drained catastrophically through the Athabasca River valley. This catastrophic flood eroded deeply into the bitumen-bearing Clearwater and McMurray Formations, transporting and then depositing bitumen in what is now the Peace-Athabasca Delta. Modern erosion of these flood deposits represents an important source of polycyclic aromatic hydrocarbons (PAHs) to the Athabasca River. This erosion occurs primarily at the Big Bend site, a large, 18 m high and 4,200 m wide cut bank, actively eroded by the Athabasca River.
    In this thesis, I estimated the contribution of the Big Bend exposure to the sediment and PAH budgets of the lower Athabasca River. The Big Bend is estimated to supply ~410 kt of sediment annually to the lower Athabasca River, which represents ~35 % of the sediment budget between Fort McMurray and the Peace-Athabasca Delta. The erosion of secondary bitumen deposits within the Big Bend exposure is estimated to contribute ~5.3 tons of PAHs to the river each year. PAHs from the Big Bend site are characterized by a unique compositional profile that can be distinguished from other PAH sources. Specifically, the secondary bitumen emplaced within the Big Bend section contains a higher alkylated PA4/PA3 ratio than other PAH sources in the lower Athabasca River region. These other sources of PAHs include primary bitumen from the McMurray Formation, as well as wildfire ash and petroleum coke, which is a by-product of bitumen upgrading. To understand the relative contribution of the various sources of PAHs to the Athabasca River, I compared these results with results from an ambient water quality monitoring program. Water samples were more similar to raw bitumen and Big Bend during months of high-flow, but matched better with forest fire ash and fluid petroleum coke during low-flow periods. These results suggest the natural bank erosion of the Athabasca River during periods of high discharge plays an important role in supplying PAHs to the lower Athabasca River and the downstream Peace-Athabasca Delta. This study has revealed that the erosion of reworked bitumen at Big Bend is a major source of PAH input to the lower Athabasca River region. This (natural) source of PAHs occurs in addition to inputs resulting from the extraction and processing of bitumen. These industrial inputs have led to increasing burdens of PAHs – and especially alkylated PAHs – across the region. Understanding the fate, biological uptake, and indeed prevalence of the various PAH sources within ecosystems and biota therefore requires additional research.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-dydt-pp59
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.